The Agri-Food & Veterinary Authority of Singapore (AVA) found that maleic acid was found in 15 out of the 66 starch-based products it tested from Taiwan. Originally, 11 products were reported as contaminated. But a recent update shows that after more testing, the number raised to 15 starch products, mostly tapioca starch balls used in bubble tea.

“AVA has informed the importers of the affected products to withdraw them from sale immediately,” AVA said in a statement.

According to Encyclopedia Britannica, maleic acid is a compound used in making polyesters for laminated moldings and paint vehicles. The AVA says that long-term exposure to the compound can lead to kidney damage, though occasional exposure causes no significant health risk. It is monitoring the situation in attempt to ensure the safety of the starch products.

Bubble tea is a mix of tea, milk, sugar, and tapioca pearls. The marble-sized pearls, or bubbles, are slightly sweet, yet with no distinct flavor, they are pulled up through the drink’s large straw to give it a soft and chewy texture.